Think your movie is an American treasure? So did 24 excluded best picture winners, says board chairman and ex-MGM exec Roger L. Mayer: "This is not a popularity contest."

The October government shutdown that led to the furlough of federal workers had an unusual side effect: It canceled the annual meeting of the National Film Preservation Board for the first time in its 25 years of existence.

Instead, the 44 members (20 active, 22 alternates, two seats vacant) who help decide which 25 films will be added to the 600 titles on the National Film Registry met via email. But the discussion leading to the mid-December reveal of the films that will be preserved in the Library of Congress was no less spirited, just as the list has prompted big debate in Hollywood for its odd inclusions and exclusions.

Classics such as Citizen Kane, Vertigo and Casablanca of course are on the list. But 24 Oscar best picture winners still aren't, including 1940's Rebecca, 1979's Kramer vs. Kramer and 1984's Amadeus. Michael Moore's seminal 1989 documentary Roger and Me? Nope. But Michael Jackson's music video Thriller made the cut, as did Gus Visser and His Singing Duck, a two-minute 1925 film that features quacking to show off how sound works in film.

"This is not a popularity contest," says National Preservation Board chairman and former MGM film exec Roger L. Mayer. "It's an attempt to tell people about the history of film and the way film portrays history."

Indeed, the board was established by the National Film Preservation Act of 1988 as an advisory body to assist the Librarian of Congress in selecting 25 "culturally, historically or aesthetically significant films" each year. The board, which includes such legends as Martin Scorsese, cinematographer Caleb Deschanel and actress Alfre Woodard, is merely advisory; librarian James Billington makes the final decisions. That hasn't stopped people in Hollywood (and their agents) from occasionally lobbying for inclusion. But board members surveyed by THR say they can't be swayed.

"This is part of our national patrimony -- this is not just about successful films," Billington says.

Half of all American films made before 1950 and more than 90 percent of films made before 1929 are lost forever. So when a film title is added to the National Film Registry, the Library of Congress works with studios, independent filmmakers and historical societies to preserve a copy at the Library. "Dr. Billington has been trying to encourage us to diversify what we nominate," says board member Matthew Bernstein, a film historian and professor at Emory University. "We're now at a point that we should be looking and championing more films that are not necessarily Hollywood mainstream."

The process actually begins with the public, who are invited to nominate films 10 years or older. For the 2012 list, 2,600 emails were sent on behalf of nearly 3,200 titles for a total of 22,500 public votes. The public support is important, says Stephen Leggett, liaison specialist/program coordinator and so-called "keeper of the list." About 75 percent of the films that eventually make the list each year were suggestions from the public. In 2001, Indianapolis Star critic Bonnie Britton suggested that Hoosiers should be added, encouraging locals to write to Billington. "It seemed like every schoolkid from that district wrote in -- and it worked," says Leggett.

But for every fan favorite that makes the list, many other modern classics -- including 1985's The Breakfast Club, 1991's Thelma & Louise and 1992's Reservoir Dogs -- have been overlooked. "As the United States changes in terms of its culture and its demographics, like most institutions, the board hasn't really kept up," says Kurt Norton, who co-directed a documentary about the National Film Registry. "But it's changing and it's doing its best."

Of the 42 active board members, 30 are men. The members are submitted by the organizations (including the MPAA, AFI, AMPAS and DGA) that hold chairs on the board, while some at-large members are invited directly by the Librarian. After meeting, each board member submits his or her final 25 picks. Then Billington -- sworn in as the 13th Librarian of Congress in 1987 and the only person to ever have this role and responsibility -- finalizes the list.

"We are the sole custodians of the copyright composite of the most creative people in human history," Billington says. "An ordinary person assumes that if it's a museum or it's in an archive, it's going to be there forever. They assume it's something that somebody else will do -- well, we're that somebody else."